The process according to the present invention relates to the removal of the impurities from the often highly impure copper sulfide melts obtained in the pyrometallurgical processing of sulfidic complex and mixed ores of copper. The great harmfulness of the impurity metals Pb, Zn, Ni, As, Sb, Bi, etc. in the pyrometallurgical refining processes of copper is generally known. These impurities are not slagged or vaporized to a sufficient degree when the ores are processed into crude metal. When crude copper is refined electrolytically these impurities greatly disturb the processing. Even very small As, Sb, Bi, and Pb amounts present in refined metal or metal alloy easily rise its heat treatment temperature very high or render the treatment impossible. These metals also have very disadvantageous effects on the other physical properties of copper and its alloys.
Certain impurities, e.g., Pb, (Ni), As, Sb, and Bi, thus cause great problems in the metallurgy of copper. In pyrometallurgical processes the compounds of these components, being easily dissociated into metals, accompany the principal metal throughout the process. Attempts are made at each stage of the process to remove these components, since if they remain in the crude metal they complicate its refining and even in very low concentrations in the final product spoil it (in conductive copper the concentrations of As, Sb, and Bi per component should be less than 0.001 % by weight).
When copper is manufactured by conventional processes (reverberatory smelting, converting, electrolysis), part of the arsenic, antimony, bismuth, lead, etc. can be removed but not to a sufficient degree. Attempts have been made continuously to develop the techniques of removing the impurities at different stages of the process.
In the production of sulfide matte the removal of the impurity components under discussion can be affected by the selection of a suitable smelting technique. Approx. 50 % of the said impurities remain in the sulfide phase in shaft, reverberatory, and electric-furnace smelting. Considerably better results are obtained in suspension processes, especially in regard to arsenic and bismuth and especially when producing mattes rich in valuable metals. Some examples of the conventional suspension processes are those according to U.S. Pat. Nos. 3,754,891, 3,790,366, 2,506,557, 3,555,164, and 3,686,656 and the processes analogous to them. In these processes the volatile heavy-metal compounds easily pass into the gas and flying-dust phases owing to the high temperature of the suspension roasting. In vertical processes the passing of the impurities (e.g., Zn, Pb, Sb) into the gas phase can be aided by means of a reduction of the suspension after the suspension roasting, e.g., according to the process described in my copending, commonly assigned U.S. application Ser. No. 682,157 filed Apr. 30, 1976. If the impurities to be vaporized are combined together with copper in stable complex structures, the dissociation of these structures and the rearrangement of the mineral lattices into simple structures promotes the vaporization of the impurities. One method for the rearrangement prior to the smelting of the concentrate is described in commonly assigned, copending U.S. application Ser. No. 587,662, filed June 17, 1975.
By means of the development in recent years it has been possible to increase the separation of the impurities under discussion per apparatus at the conversion stage from the conventional values (70-75 %) to values above 90 %. The separation has been improved by, for example, combining the impurities by oxidizing them with alkali or iron oxides into stable compounds separable from the melt. One of the processes is that according to U.S. Pat. 3,744,922, in which antimony is combined with iron in a mixed spinel lattice. When copper and copper-nickel (&lt;28 % Ni) mattes are converted, the metal melt with a low sulfur content separates from the sulfide matte as a phase of its own owing to the melt solubility gap between the sulfide and the metal phases. This produced metal "preliminary drop" contains, owing to the activity conditions in the M3--MeS systems, a great number of various concentrated components (Ag, Au, Pd, Sn, As, Sb, Bi, etc.). The said components can be substantially decreased in the principal melt by separating this "preliminary drop" at the initial stage of the sulfide oxidation. Some examples of these processes are those described in U.S. Pat. No. 2,425,760 and DT-PS No. 1,922,599.
In recent years, attempts have also been made to remove the impurities from a sulfide melt by developed vacuum or gas vacuum processes (e.g., H. Kametani et al., Trans. JIM, 14, 1973, 218-223).
Processes according to the new process under discussion, based on a chlorinating vaporization of the impurities from a copper sulfide melt, are most likely not known. This is because copper readily becomes chlorinated along with the impurities. The chlorination of solid sulfide concentrates (Cu, Zn, Pb, Ag, Ni, Co, Sn, etc.) in order to recover valuable metals is, however, well known as a process of low temperatures (e.g., J. Garlach et al.: Trans. AIME, 239, 1967, 1557; Erzmetall, 21, 1968, 9). The chlorination of the sulfide matte of nickel by means of both gaseous chlorine and the chloride of nickel by using salt melts is known. Thereby the impurities (e.g., Cu, Pb, Sn, Co, Fe, As, Sb) are removed from molten nickel matte. Some examples of descriptions of the process are those in U.S. Pat. Nos. 3,660,026, 3,802,870, and M. C. Bell et al.: Purification of Nickel Matte (103rd AIME Annual Meeting, Dallas Tex., Feb. 24-28, 1974, 1-18).
It should be noted that the technique used for the prepurification of the crude metal in an anode furnace is the same as in conversion. Some of the different processes are the selective oxidation of the impurities with earth-alkali oxides, the binary-salt processes (DT-PS No. 1,137,223), the oxidation of melt with copper oxide (As, Sb, and Bi: Jap. 19032-3 (1969)), and the vacuum methods (e.g., J. Bocle et al.: Erzmetall, 24, 1971, 480). Halogen salt vaporization is also used for the purification of cement copper in molten state (AlNs.sub.3 F.sub.6 : U.S. Pat. No. 3,630,722).